JP5018670B2 - Single crystal growth method - Google Patents

Description

  The present invention relates to a method for pulling and growing a single crystal of a semiconductor raw material such as silicon by the Czochralski method (hereinafter referred to as CZ method).

Conventionally, as a method for growing this type of single crystal, a crucible filled with a raw material melt of the single crystal, a pulling means for growing the single crystal by bringing the seed crystal into contact with the surface of the melt, and a pulling region of the single crystal A method of pulling a single crystal is disclosed using an apparatus that includes a rectifying jig that surrounds the periphery and shields radiant heat and regulates the flow of an inert gas (see, for example, Patent Document 1). In this single crystal pulling method, when the seed crystal is brought into contact with the melt surface in the crucible and the neck portion is formed, the gap (distance (1)) between the lower end of the rectifying jig and the melt surface is set to 30 to 30. After setting the neck portion of the single crystal to a diameter of 6 to 15 mm and making the crystal dislocation-free, the gap (distance (2)) between the lower end of the rectifying jig and the melt surface is set to 15 to 30 mm. After that, a single crystal shoulder is formed, and then the body part is grown. In this single crystal pulling method, a gap (distance (1)) increased in the stage of forming the neck is used to form a neck that can prevent the dislocation of the single crystal and prevent the fall of the single crystal. When shifting to pulling, various growth conditions can be selected by selecting a gap to be adopted (distance (2)). As a result, even when pulling a heavy single crystal, by changing the gap in the pulling process, the single crystal can be grown without dislocation and can be safely pulled without causing a fall accident. It has become.
Japanese Patent No. 3698080 (Claim 1, paragraph [0021], paragraph [0044])

However, in the pulling method of the single crystal shown in the above-mentioned conventional Patent Document 1, although the gap is increased before the seed crystal is immersed in the melt, the gap is reduced during the growth of the neck portion. There is a problem that the neck becomes long and the chamber becomes long or the pulling length of the single crystal is limited.
An object of the present invention is to provide a method for growing a single crystal, which can prevent the chamber from becoming long by preventing the neck portion from becoming long, and can prevent the pulling length of the single crystal from being limited. It is to provide.

According to the first aspect of the present invention, the melt is stored in a crucible housed in a chamber, a seed crystal is immersed in the melt and pulled up to grow a single crystal, and further provided above the melt surface. This is an improvement of the method for growing a silicon single crystal in which the thermal shield surrounds the outer peripheral surface of the growing single crystal and shields the irradiation of the radiant heat to the outer peripheral surface of the single crystal by the heater. The characteristic configuration is that the crucible is lowered or the heat shield is raised so that the gap between the melt surface and the lower end of the heat shield is 50 mm to 200 mm, and then the seed crystal is immersed in the melt surface. While growing the neck of the single crystal and growing the shoulder of the single crystal from the melt surface, the crucible is raised or the heat shield is lowered so that the gap is 15 mm to 100 mm. .
The invention according to claim 2 is the invention according to claim 1, wherein the thermal shield is fixed to the chamber, and the gap between the melt surface and the lower end of the thermal shield is adjusted by raising and lowering the crucible, so that the shoulder of the single crystal During the growth of the part, the crucible is raised at a speed slower than the pulling speed of the seed crystal to bring the melt surface closer to the lower end of the heat shield.

  In the invention according to claim 1, since the gap is made small at the time of growing the neck portion, there is a problem that the neck portion becomes long and the chamber becomes long or the pulling length of the single crystal is limited. Compared with the conventional pulling method of the single crystal, in the present invention, since the gap is reduced during the growth of the shoulder portion, it is possible to prevent the neck portion from becoming long. As a result, in the present invention, it is possible to prevent the chamber from becoming long, and to prevent the pulling length of the single crystal from being limited.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, the growth apparatus 10 for a silicon single crystal 11 includes a water-cooled chamber 12 capable of adjusting the internal pressure, and a crucible 13 provided in the chamber 12. The chamber 12 has a large-diameter bottomed cylindrical main chamber 12a and a small-diameter cylindrical pull chamber 12b connected to the upper end of the main chamber 12a, and the crucible 13 is accommodated in the main chamber 12a. The crucible 13 includes a bottomed cylindrical inner layer container 13a formed of quartz and storing the silicon melt 14, and a bottomed cylindrical outer layer container 13b formed of graphite and fitted to the outside of the inner layer container 13a. It consists of. The upper end of the shaft 16 is connected to the bottom surface of the outer layer container 13b, and a crucible driving means 17 for rotating and raising / lowering the crucible 13 through the shaft 16 is provided at the lower portion of the shaft 16. Further, the outer peripheral surface of the crucible 13 is surrounded by a resistance heating type cylindrical heater 18 at a predetermined interval, and the outer peripheral surface of the heater 18 is surrounded by a cylindrical heat insulating cylinder 19 at a predetermined interval. In this embodiment, a silicon melt is used as the melt, and a silicon single crystal is used as the single crystal. However, a GaAs melt and a GaAs single crystal, an InP melt and an InP single crystal, a ZnS melt and a ZnS single crystal are used. A crystal, or a ZnSe melt and a ZnSe single crystal may be used.

  On the other hand, a seed pulling means 21 is provided at the upper end of the pull chamber 12b. The seed pulling means 21 is configured to move up and down a pulling shaft 21a whose lower end reaches the surface of the silicon melt 14 in the crucible 13. The pulling shaft 21a is configured to rotate around the axis of the pulling shaft 21a by a seed rotating means (not shown) together with the seed pulling means 21. Further, a seed chuck 22 is provided at the lower end of the pulling shaft 21a, and this chuck 22 is configured to hold the seed crystal 23. The pulling shaft 21a is constituted by a wire or a pulling rod. An inert gas consisting only of argon gas is circulated in the main chamber 12a. The inert gas is introduced into the pull chamber 12b through a gas supply pipe (not shown) connected to the side wall of the pull chamber 12b, and passes through a gas discharge pipe (not shown) connected to the lower wall of the main chamber 12a. And is configured to be discharged out of the main chamber 12a. A heat shield 24 is provided in the main chamber 12a to block the irradiation of the radiant heat of the heater 18 to the outer peripheral surface of the silicon single crystal 11 and to rectify the inert gas. The heat shield 24 has a truncated cone-shaped cylinder that gradually decreases in diameter as it goes downward and surrounds the outer peripheral surface of the silicon single crystal 11 pulled up from the silicon melt 14 at a predetermined interval from the outer peripheral surface. 24a and a flange portion 24b that is connected to the upper edge of the cylindrical body 24a and projects outward in a substantially horizontal direction. Further, the heat shield 24 is configured such that the flange 24b is placed on the heat retaining cylinder 19 via the ring plate 24c so that the lower edge of the cylinder 24a is spaced upward from the surface of the silicon melt 14 with a predetermined gap G. It is fixed in the main chamber 12a so as to be positioned. This gap G is adjusted by raising and lowering the crucible 13 by the crucible driving means 17. The gap may be adjusted not by raising or lowering the crucible but by raising and lowering the heat shield. In this case, the heat shield is configured to be raised and lowered by the heat shield driving means.

  The upper outer surface of the main chamber 12a has a boundary between the silicon melt 14 and the seed crystal 23, a boundary between the silicon melt 14 and the neck 11a, a boundary between the silicon melt 14 and the shoulder 11b, or silicon. A two-dimensional CCD camera 26 is installed so as to face a solid-liquid interface that is a boundary portion between the melt 14 and the straight body portion. The two-dimensional CCD camera 26 has a solid-liquid interface when the seed crystal 23 is immersed in the silicon melt 14 or when the neck portion 11a, the shoulder portion 11b, the straight body portion, and the tail portion are pulled up from the silicon melt 14. Configured to shoot height. Here, the two-dimensional CCD camera 26 accumulates signal charges generated by light in a capacitor formed by arranging electrodes of a metal film on a semiconductor substrate via an oxide film, and a drive pulse from the image processing means 27. The camera obtains an image signal that is an electric signal by sequentially transferring the image signal in one direction. The two-dimensional image taken by the two-dimensional CCD camera 26 is processed by the image processing means 27. The detection output of the two-dimensional CCD camera 26 is connected to the camera control input of the image processing means 27, and the camera control output of the image processing means 27 is connected to the control input of the two-dimensional CCD camera 26. The control input / output of the image processing means 27 is connected to the control input / output of the controller 28, and the control output of the controller 28 is connected to the heater 18, the seed pulling means 21, the seed rotating means and the crucible driving means 17.

  A method for growing the silicon single crystal 11 using the growth apparatus 10 configured as described above will be described. First, after reducing the pressure in the chamber 12, an inert gas such as argon gas is introduced to create a reduced inert gas atmosphere in the chamber 12, and the crystal raw material in the crucible 13 is melted by the heater 18. Next, while the pulling shaft 21a is on the same axis as the axis of the shaft 16 and is rotated at a predetermined speed in the direction opposite to the rotation direction of the shaft 16, the seed crystal 23 attached to the seed chuck 22 is lowered and its tip is moved. The part is positioned immediately above the surface of the silicon melt 14. In this state, the crucible 13 is lowered by the crucible driving means 17 so that the gap G between the silicon melt 14 and the lower end of the heat shield 24 is 50 mm to 200 mm, preferably 70 mm to 150 mm (FIG. 1). Here, the gap G between the silicon melt 14 before immersing the seed crystal 23 in the silicon melt 14 and the lower end of the heat shield 24 is limited to the range of 50 mm to 200 mm. There is a possibility that dislocation is introduced into the seed crystal 23 because the temperature difference between the seed crystal 23 and the seed crystal 23 is too large. This is because there is a risk of deformation. The liquid surface position of the silicon melt 14 stored in the crucible 13 is an image that is an electric signal when the image processing means 27 transmits a drive pulse to the two-dimensional CCD camera 26 to scan the two-dimensional CCD camera 26. The signal is taken in, and the controller 28 detects the liquid level position of the silicon melt 14 from the image signal.

  Thereafter, the seed crystal 23 is immersed in the surface of the silicon melt 14 to grow the neck portion 11 a of the silicon single crystal 11. When the seed crystal 23 is immersed in the surface of the silicon melt 14, the seed crystal 23 is efficiently heated by the radiant heat of the heater 18 from the large gap G, so that the temperature of the silicon melt 14 is lower than the temperature of the silicon melt 14. The temperature difference is 100 ° C. or less, preferably 70 ° C. or less. For this reason, the thermal stress at the time of immersion of the seed crystal 23 in the silicon melt 14 can be reduced, and dislocations are hardly introduced into the seed crystal 23. Further, by increasing the gap G, the temperature gradient at the neck portion 11a is reduced, the isotherm is close to a flat surface, the temperature gradient in the radial direction at the neck portion 11a is reduced, and the thermal stress in the neck portion 11a is reduced. Since the dislocation motion speed is reduced at the same time as dislocation is reduced, the dislocation removal capability at the neck portion 11a increases. As a result, dislocations can be removed even when the diameter of the neck portion 11a is increased, and the silicon single crystal 11 having an increased weight can be grown without propagating the dislocations. Specifically, a relatively thick neck portion 11a having a diameter of 5 mm to 10 mm can be grown.

  Next, the process proceeds to the growth of the shoulder portion 11b of the silicon single crystal 11, and the crucible 13 is raised so that the gap G is 15 mm to 100 mm, preferably 25 mm to 80 mm while the shoulder portion 11b is grown ( Figure 2). That is, during the growth of the shoulder 11b of the silicon single crystal 11, the crucible 13 is raised at a speed slower than the pulling speed of the seed crystal 23, thereby bringing the surface of the silicon melt 14 closer to the lower end of the heat shield 24 and reducing the gap G. To do. Normally, when the shoulder portion 11b of the silicon single crystal 11 is grown without changing the gap G, the crucible 13 is pushed up by the silicon melt 14 reduced by the growth of the shoulder portion 11b as shown by the broken line in FIG. Thus, the surface of the silicon melt 14 is held at a certain height. On the other hand, in order to grow the shoulder 11b of the silicon single crystal 11 while reducing the gap G, the gap G decrease at the time of growing the shoulder 11b was added to the silicon melt 14 minutes reduced by the growth of the shoulder 11b. The crucible is pushed up at a speed (substantially trapezoidal portion of the two-dot chain line in FIG. 3), and the pulling speed of the seed crystal 23 is made higher than the rising speed of the crucible 13 for growth of the shoulder 11b (shown by the solid line in FIG. 3). (Substantially convex part). In FIG. 3, when the shoulder portion 11b is grown, the rising speed of the crucible 13 is changed to a substantially trapezoidal shape, and the pulling speed of the seed crystal 23 is changed to a substantially convex shape to suppress rapid speed fluctuations. Because.

  Thus, during the growth of the shoulder portion 11b of the present embodiment, the reason why the rising speed of the crucible 13 is changed to a substantially trapezoidal shape and the pulling speed of the seed crystal 23 is changed to a substantially convex shape is that of the conventional shoulder portion. A specific explanation will be given in comparison with the ascending speed of the crucible and the pulling speed of the seed crystal during growth. When the adjustment to reduce the gap G at the conventional neck portion is not performed, first, the growth process of the small-diameter neck portion shifts from the state where the pulling rate of the seed crystal is high to the shoulder growth step. At this time, in order to increase the diameter of the silicon single crystal, the pulling rate of the seed crystal and the temperature of the silicon melt are lowered. However, the effect of lowering the temperature of the silicon melt does not appear immediately. When the effect of lowering the temperature of the silicon melt appears, the pulling rate of the seed crystal is gradually increased (portion shown by (1) in FIG. 4) to prevent the diameter of the shoulder from being excessively expanded. Next, when the equilibrium state is reached, the pulling speed of the seed crystal is kept almost constant (portion (2) in FIG. 4). Thereafter, the temperature of the silicon melt is raised to suppress the expansion of the diameter of the shoulder portion, and the pulling rate of the seed crystal is lowered (the portion indicated by (3) in FIG. 4) to match the diameter of the straight body portion to be grown. The ascending speed of the crucible is set so as to always keep the surface of the silicon melt at a predetermined height.

  On the other hand, when the gap G is adjusted to be reduced by the shoulder portion 11b of the present embodiment, first, the growth step of the shoulder portion 11b from the state in which the pulling speed of the seed crystal 23 is high in the growth step of the small-diameter neck portion 11a. Migrate to At this time, in order to increase the diameter of the silicon single crystal 11, the pulling speed of the seed crystal 23 and the temperature of the silicon melt 14 are lowered. However, the effect of lowering the temperature of the silicon melt 14 does not appear immediately. When the effect of lowering the temperature of the silicon melt 14 appears, the pulling speed of the seed crystal 23 and the rising speed of the crucible 13 are increased relatively rapidly ((1-1) and (2-1 in FIG. 3). ), The rate of increase of the pulling rate of the seed crystal 23 is moderated (portion indicated by (1-2) in FIG. 3), and the rising rate of the crucible 13 is kept substantially constant (in FIG. 3). (Part indicated by (2-2)), preventing the diameter of the shoulder portion 11b from expanding too much. Next, when the equilibrium state is reached, the pulling speed of the seed crystal 23 is kept substantially constant (portions indicated by (1-3) and (2-2) in FIG. 3). Thereafter, the temperature of the silicon melt 14 is raised to prevent the diameter of the shoulder 11b from expanding, and the pulling speed of the seed crystal 23 and the rising speed of the crucible 13 are lowered (see (1-4) and (2- 3) Match the diameter of the straight body to be grown. As a result, the gap G becomes a predetermined small value. It should be noted that the final gap G that was reduced during the growth of the shoulder portion 11b, that is, the gap G when the straight body portion was grown was limited to the range of 15 mm to 100 mm. This is because the silicon single crystal 11 is easily broken by being rapidly cooled, and when the thickness exceeds 100 mm, the silicon single crystal 11 is gradually cooled and it is difficult to grow the silicon single crystal 11.

  Further, after the straight body portion of the silicon single crystal 11 is grown, the diameter of the silicon single crystal 11 is gradually reduced so that high-density dislocations are not introduced into the silicon single crystal 11 due to a rapid temperature change. The tail portion is formed by gradually lowering the temperature of the silicon single crystal 11 to separate the silicon single crystal 11 from the silicon melt 14. Thereafter, the pulling of the silicon single crystal 11 is completed by cooling. Therefore, since the gap is reduced during the growth of the neck portion, the neck portion becomes longer, the chamber becomes longer, or the pulling length of the silicon single crystal is limited. Compared with the pulling method, in the present embodiment, the gap G is reduced during the growth of the shoulder portion 11b, so that the neck portion 11a can be prevented from becoming longer. As a result, in the present embodiment, it is possible to prevent the chamber 12 from becoming long and to prevent the pulling length of the silicon single crystal 11 from being limited.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
A silicon single crystal 11 having a diameter of 308 mm was grown using the growth apparatus 10 shown in FIGS. Specifically, first, the pressure inside the chamber 12 is reduced, and then an inert gas atmosphere such as argon gas is introduced to reduce the pressure inside the chamber 12, and the crystal raw material in the crucible 13 is melted by the heater 18. . Next, while the pulling shaft 21a is on the same axis as the axis of the shaft 16 and is rotated at a predetermined speed in the direction opposite to the rotation direction of the shaft 16, the seed crystal 23 attached to the seed chuck 22 is lowered and its tip is moved. The part was positioned immediately above the surface of the silicon melt 14. In this state, the crucible 13 was lowered by the crucible driving means 17 so that the gap G between the silicon melt 14 and the lower end of the heat shield 24 was 150 mm (FIG. 1). Although the temperature of the seed crystal 23 is lower than the temperature of the silicon melt 14, when the temperature difference reaches 70 ° C., the seed crystal 23 is immersed in the surface of the silicon melt 14 and the neck portion of the silicon single crystal 11. 11a was grown. The diameter of the neck part was 6.5 mm. Next, it shifted to the growth of the shoulder portion 11b of the silicon single crystal 11, and while the shoulder portion 11b was grown, the crucible 13 was raised so that the gap G was 80 mm (FIG. 2). A profile of the pulling speed of the seed crystal 23 and the rising speed of the crucible 13 at this time is shown in FIG. Further, after the straight body portion of the silicon single crystal 11 was grown, the diameter of the silicon single crystal 11 was gradually reduced to form a tail portion, and the silicon single crystal 11 was separated from the silicon melt 14. This silicon single crystal 11 was taken as Example 1.

<Comparative Example 1>
As in Example 1, before immersing the seed crystal in the silicon melt, the crucible is lowered so that the gap G between the silicon melt and the lower end of the heat shield is 150 mm, and the temperature of the seed crystal is changed to the silicon melt. When the temperature difference reached 70 ° C., the seed crystal was immersed in the surface of the silicon melt to grow the neck portion 11a of the silicon single crystal. The crucible was raised so that the gap G was 80 mm during the latter half of the neck. Next, it shifted to the growth of the shoulder portion of the silicon single crystal, and the gap G was kept constant (80 mm) during the growth of the shoulder portion. A profile of the pulling rate of the seed crystal and the rising rate of the crucible at this time is shown in FIG. Further, after growing a straight body portion of the silicon single crystal, similarly to Example 1, the diameter of the silicon single crystal was gradually reduced to form a tail portion, and the silicon single crystal was separated from the silicon melt. This silicon single crystal was designated as Comparative Example 1.

<Comparison test and evaluation>
When the total length of the silicon single crystal of Example 1 and Comparative Example 1 including the neck portion, shoulder portion, straight body portion and tail portion was measured, the total length of the silicon single crystal of Comparative Example 1 was as long as 3000 mm, The total length of the silicon single crystal of Example 1 was as short as 2500 mm.

It is a longitudinal section lineblock diagram showing the state where the neck part of the silicon single crystal of the embodiment of the present invention is pulled up. It is a longitudinal cross-section block diagram corresponding to FIG. 1 which shows the state which has pulled up the shoulder part of the silicon single crystal. It is a figure which shows the change of the pulling-up speed of a silicon single crystal, and the raising speed of a crucible with respect to the change of the pulling length of the shoulder part of the silicon | silicone single crystal of embodiment and Example 1. FIG. It is a figure which shows the change of the pulling-up speed of a silicon single crystal, and the raising speed of a crucible with respect to the change of the pulling length of the shoulder part of the silicon single crystal of a prior art example and the comparative example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Silicon single crystal 11a Neck part 11b Shoulder part 12 Chamber 13 Crucible 14 Silicon melt 18 Heater 23 Seed crystal 24 Heat shield

Claims (2)

A melt is stored in a crucible accommodated in a chamber, a seed crystal is immersed in the melt and pulled up to grow a single crystal, and a heat shield provided above the melt surface further grows the crystal. In the method for growing a silicon single crystal that surrounds the outer peripheral surface of the single crystal and shields the irradiation of radiant heat to the outer peripheral surface of the single crystal by a heater,
After lowering the crucible or raising the heat shield so that the gap between the melt surface and the lower end of the heat shield is 50 mm to 200 mm, the seed crystal is immersed in the melt surface. Growing the neck of the single crystal;
While growing the shoulder portion of the single crystal from the melt surface, the crucible is raised or the heat shield is lowered so that the gap is 15 mm to 100 mm. How to train.   The thermal shield is fixed to the chamber, and the gap between the melt surface and the lower end of the thermal shield is adjusted by raising and lowering the crucible. The method for growing a single crystal according to claim 1, wherein the melt surface is brought close to the lower end of the heat shield by raising.

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